The present invention relates to automatic transmission systems and, more particularly, to an improved Pressure Regulator Valve Assembly for Ford E40D transmissions.
Automatic transmission systems of the prior art have a hydraulic circuit subsystem which includes at least a hydraulic pump, a valve body having fluid conducting passages or circuits, input and exhaust ports formed within the fluid circuits, and a plurality of so-called spool valves comprised of generally cylindrical pistons having control diameters or lands formed thereon, which alternately open and close the ports to the fluid circuits to regulate the flow and pressure of automatic transmission fluid (hereinafter xe2x80x9cATFxe2x80x9d). It will be understood that in describing hydraulic fluid circuits, ATF usually changes names when it passes through an orifice or control valve in a specific circuit.
Pumps in automatic transmission systems are generally positive displacement pumps driven by the engine of the vehicle wherein the transmission is installed. A positive displacement pump is one, which has the same output per revolution regardless of pump speed or pressure already developed in the system. Thus, it is necessary to regulate ATF pressure so it does not get too high or too low and damage other components.
A basic pressure regulator employs a piston and a spring that compresses at a specific pressure to allow some ATF to flow back to the pump reservoir or sump bypassing the hydraulic circuits and reducing pressure. By using a pressure regulator with a spring calibrated to a pressure lower than the pump""s output, constant pressure can be maintained in the system during operation.
Vehicles with Ford E40D transmissions often have service complaints of the torque converter overheating and high line pressure, which is attributable, in part, to the design of the original equipment manufacture (hereinafter xe2x80x9cOEMxe2x80x9d) Main Regulator Valve. When in the Park gear range and at low speeds, the Ford E40D Main Regulator Valve is designed to feed adequate ATF to the torque converter and transmission cooler circuits. However, at higher speeds and/or under high EPC solenoid pressure, ATF flow to the torque converter charge circuit and cooler circuits can be shut down by the Main Regulator Valve resulting in torque converter overheating.
Another contributing factor to the torque converter overheating problem is that the OEM balance circuit for the Main Regulator Valve does not provide sufficient ATF flow to properly counteract EPC solenoid pressure, which tends to keep the Main Regulator Valve in the high line position restricting ATF feed to the torque converter and cooler circuits.
There are several known prior art patents that are available in the field and their discussion follows. One example is U.S. Pat. No. 4,271,939 to Iwanga et al., which discloses a hydraulic control system for a torque converter for ensuring release of the lock-up condition of the torque converter. This is accomplished by providing a flow restrictor in the hydraulic working fluid supply passage for the torque converter to make the flow resistance of the passage equal to or larger than the flow resistance of the hydraulic working fluid supply passage for the lock-up control chamber. In this control system a first or feed passageway communicates with a source of pressurized fluid and with a torque converter chamber, a second or discharge passageway communicates with the torque converter chamber and a third passageway communicates with a lock-up control or clutch chamber of the lockup clutch. A lockup control valve communicates with the same source of pressurized fluid and with the third passageway. The first passageway is provided with the flow restrictor. With the provision of the flow restrictor, the disengagement of the lockup clutch will be assured upon pressurization of the third passageway.
Another example is U.S. Pat. No. 4,618,036 to Ideta, which discloses a hydraulic control system for the lockup clutch of a torque converter wherein release of a lockup clutch is ensured even when the discharge flow rate of the pump is low. This control system comprises a pump driven by an engine to discharge fluid, a torque converter having a lockup clutch with a lockup clutch piston movable to a clutch released position when fluid pressure within a lockup release chamber is higher than fluid pressure within a working chamber in the torque converter cavity, a line pressure regulator valve and an orifice, which provides a restricted flow communication between the torque converter and the pump even when line pressure generated by the line pressure regulator valve is lower than a predetermined value.
The Ideta (""036) patent utilizes cutouts 20 formed on the land 32d of the first spool 32 (FIG. 1) on the line pressure regulator valve to permit a sufficient flow of hydraulic fluid via oil conduit 62 to torque converter 10 at low speed operation to ensure the release of the lockup clutch.
The present invention provides a Pressure Regulator Valve Assembly having advantages over the prior art. The present invention is a replacement Pressure Regulator Valve Assembly for maintaining a continuous flow of hydraulic fluid to the torque converter in all operating modes of an automatic transmission such as the Ford E40D and other similar transmissions to prevent torque converter overheating.
Accordingly, the present Pressure Regulator Valve Assembly includes a valve piston subassembly having an encapsulated internal check valve in fluid communication with the line pressure circuit, which diverts ATF to the torque converter charge circuit responsive to a lower fluid pressure (i.e. 2-5 psi) than is required to fill the torque converter under normal operating conditions. Thus, at high pressure conditions and during torque converter release an adequate ATF level is maintained in the torque converter to prevent overheating.
When the vehicle engine is shut off the internal check valve also prevents ATF from draining back through the Pressure Regulator Valve to the sump to maintain an adequate ATF level in the torque converter at engine startup. In addition, a Balance Boost fluid circuit has been added to the present Pressure Regulator Valve to assist the OEM Balance circuit in counteracting the electronic pressure control (EPC) solenoid pressure.
The present Pressure Regulator Valve is a direct replacement for the OEM Main Regulator Valve that is standard equipment on Ford E40D transmission, which will be referred to throughout this specification.
There has thus been outlined, rather broadly, the important features of the invention in order that the detailed description thereof that follows may be better understood, and in order that the present contribution to the art may be better appreciated.
Other features and technical advantages of the present invention will become apparent from a study of the following description and the accompanying drawings.